Moisture-absorbing core-sheath composite yarn, and fabric

ABSTRACT

A moisture-absorbing core-sheath composite yarn has a sheath polymer made of a polyamide, a core polymer is a polyetheresteramide copolymer, and the strength retention after a 150° C. 1-hour dry heat treatment is 50% or higher. The core-sheath composite yarn has high moisture-absorbing performance, is more comfortable than natural fibers, and can retain the soft texture, durability, and moisture-absorbing/releasing performance even when laundered and dried repeatedly.

TECHNICAL FIELD

This disclosure relates to a hygroscopic core-sheath composite yarn and fabric.

BACKGROUND

Synthetic fibers made of thermoplastic resins including polyamide and polyester are widely used for clothing and industrial applications because of being high in strength, chemical resistance, heat resistance and the like.

In particular, in addition to its unique characteristics including softness, high tensile strength, coloring property in dyeing processes, and high heat resistance, polyamide fiber is so high in hygroscopicity that it is widely used for applications such as inner wear and sports wear. However, polyamide fibers are not sufficiently hygroscopic compared to natural fibers such as cotton and have some problems such as undesired stuffiness and stickiness, leading to inferior comfortability to natural fibers.

Against this background, synthetic fibers showing excellent moisture absorbing and releasing properties that prevent stuffiness and stickiness and having comfortability similar to that of natural fibers are now demanded mainly for innerwear and sports apparel applications.

Then, the addition of a hydrophilic chemical compound to a polyamide fiber has been studied most widely. For example, Japanese Unexamined Patent Publication (Kokai) No. HEI 09-188917 proposes a method of improving hygroscopic performance by blending polyvinylpyrrolidone, used as a hydrophilic polymer, with polyamide, followed by spinning.

On the other hand, there have been many studies that attempt to produce fibers having a core-sheath structure composed mainly of a highly hygroscopic thermoplastic resin as the core component and a thermoplastic resin with excellent mechanical properties as the sheath component, in an attempt to provide a fiber having both high moisture absorbing performance and good mechanical properties.

For example, International Publication WO 2014/10709 discloses a core-sheath composite fiber composed mainly of a core component and a sheath component such that the core component is not exposed in the fiber surface. In this core-sheath composite fiber, the core component is a polyether block amide copolymer containing 6-nylon as a hard segment whereas the sheath component is a 6-nylon fiber, wherein the area ratio between the core component and the sheath component in the cross section of the fiber is 3/1 to 1/5.

Japanese Unexamined Patent Publication (Kokai) No. HEI 06-136618 discloses a sheath-core type composite fiber containing a thermoplastic resin as the core component and a fiber-forming polyamide resin as the sheath component, wherein the main constituent of the thermoplastic resin in the core component is a polyether ester amide, the core component accounting for 5% to 50% by weight of the total weight of the composite fiber. The document describes a highly hygroscopic core-sheath type composite fiber with the above feature containing polyether ester amide as the core component and polyamide as the sheath component.

In addition, Japanese Unexamined Patent Publication (Kokai) No. HEI 08-209450 describes a composite fiber having moisture absorbing and releasing properties characterized by containing polyamide or polyester as the sheath component and a thermoplastic water absorbing resin made of crosslinked polyethylene oxide as the core component. The document mentions a highly hygroscopic core-sheath composite fiber containing a highly hygroscopic water-insoluble modified polyethylene oxide as the core component and polyamide as the sheath component.

However, although having moisture absorbing and releasing properties similar to those of natural fibers, the fiber described in JP '917 does not have satisfactorily high performance, and the achievement of better moisture absorbing and releasing properties is still a problem to be solved.

In addition, although having moisture absorbing and releasing properties as good as or better than those of natural fibers, the core-sheath composite fibers described in WO '709, JP '618 and JP '450 tend to suffer from thermal degradation of the core component and hardening of the fibers as they undergo frequent washing and drying in household type machines, causing the fabrics to suffer from hardening of the texture, a decrease in durability, or deterioration in moisture absorbing and releasing performance.

SUMMARY

We thus provide:

-   (1) A hygroscopic core-sheath composite yarn including polyamide as     the sheath polymer and a polyether ester amide copolymer as the core     polymer and characterized by having a strength retention rate of 50%     or more after undergoing dry heat treatment at 150° C. for 1 hour. -   (2) A hygroscopic core-sheath composite yarn as set forth in     paragraph (1) having a ΔMR value of 5.0% or more and a ΔMR retention     rate of 70% or more after undergoing dry heat treatment at 150° C.     for 1 hour. -   (3) A fabric containing, at least partly, a hygroscopic core-sheath     composite yarn as set forth in either paragraph (1) or (2).

We provide a core-sheath composite yarn that is high in hygroscopic performance, higher in comfortability than natural fibers, and able to maintain a soft texture, high durability, and moisture absorbing and releasing performance after undergoing repeated washing and drying.

DETAILED DESCRIPTION

Our core-sheath composite yarn includes polyamide as the sheath component and a polyether ester amide copolymer as the core component.

The polyether ester amide copolymer is a block copolymer having an ether bond, an ester bond, and an amide bond in one molecular chain. More specifically, the block copolymer polymer which can be produced by subjecting one, two, or more selected from the group consisting of lactams, aminocarboxylic acids, and salts of diamine and dicarboxylic acid, referred to polyamide component (A), and a polyether ester component (B) formed of a dicarboxylic acid and a poly(alkylene oxide) glycol to condensation polymerization reaction.

Substances suitable as the polyamide component (A) include lactams such as ε-caprolactam, dodecanolactam, and undecanolactam; ω-aminocarboxylic acids such as aminocaproic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid; and nylon salts of diamine-dicarboxylic acids that serve as precursors of nylon 66, nylon 610, nylon 612 and the like, of which ε-caprolactam is preferred as polyamide-forming component.

The polyether ester component (B) is formed of a dicarboxylic acid containing 4 to 20 carbon atoms and a poly(alkylene oxide) glycol. Examples of the dicarboxylic acid containing 4 to 20 carbon atoms include aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, and dodecanoic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and 2,6-naphthalene dicarboxylic acid; and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid that may be used singly or as a mixture of two or more thereof. Preferable dicarboxylic acids include adipic acid, sebacic acid, dodecanoic acid, terephthalic acid, and isophthalic acid. Examples of the poly(alkylene oxide) glycol include polyethylene glycol, poly(1,2- or 1,3-propylene oxide) glycol, poly(tetramethylene oxide) glycol, and poly(hexamethylene oxide) glycol, of which polyethylene glycol is preferable because of having high hygroscopic performance.

It is preferable for the poly(alkylene oxide) glycol to have a number average molecular weight of 300 to 3,000, more preferably 500 to 2,000. A molecular weight of 300 or more is preferable because scattering out of the system during condensation polymerization reaction can be prevented to ensure the formation of a fiber with stable hygroscopic performance. A molecular weight of 3,000 or less is preferable because the poly(alkylene oxide) glycol can be dispersed uniformly in the polymer to ensure high hygroscopic performance.

Regarding the component percentage of the polyether ester component (B), it preferably accounts for 20% to 80% by mole of the total quantity of the polyether ester amide copolymer. A percentage of 20% or more is preferable because high hygroscopic performance can be realized. On the other hand, a percentage of 80% or less is preferable to ensure high dyed color fastness and little hygroscopic performance deterioration by washing.

The component percentages of the polyamide and poly(alkylene oxide) glycol are preferably 20%/80% to 80%/20% by mole. A poly(alkylene oxide) glycol content of 20% or more is preferable because high hygroscopic performance can be realized. On the other hand, a poly(alkylene oxide) glycol preferably content of 80% or less is preferable to ensure high dyed color fastness and little hygroscopic performance deterioration by washing.

Commercially available products of such a polyether ester amide copolymer include MH1657 and MV1074 manufactured by Arkema K.K.

Examples of the polyamide used as the sheath component include nylon 6, nylon 66, nylon 46, nylon 9, nylon 610, nylon 11, nylon 12, and nylon 612; and copolymer polyamides containing, as a copolymer component, a compound having a functional group that can form an amide with the former such as laurolactam, sebacic acid, terephthalic acid, isophthalic acid, and 5-sodium sulfoisophthalic acid. In particular, nylon 6, nylon 11, nylon 12, nylon 610, and nylon 612 are preferable from the viewpoint of yarn-making performance because they are small in the difference in melting point from the polyether ester amide copolymer, serving to depress the thermal degradation of the polyether ester amide copolymer during melting spinning. Of these, nylon 6 is particularly preferable because of high dyeability.

It is essential for the core-sheath composite yarn to have a strength retention rate of 50% or more and 100% or less after undergoing dry heat treatment at 150° C. for 1 hour. If it is less than 50%, the raw threads will become hard and brittle and a fabric test piece will decrease in durability and suffer breakage or the like when subjected to repeated drying test in a household washing and drying machine (hereinafter referred to as tumble drying). It is preferably 60% or more and 100% or less. If it is in this range, it will be possible to produce clothing that can maintain durability after repeated tumble drying.

It is preferable for the core-sheath composite yarn to have a tensile strength of 2.5 cN/dtex or more. It is more preferably 3.0 cN/dtex or more. If it is in this range, it will be possible to produce clothing that are high enough in strength to serve for practical clothing uses such as innerwear and sports apparel applications.

It is essential for the core-sheath composite yarn to maintain controlled humidity in clothing to ensure high comfortability when they are worn. The degree of humidity control is examined based on ΔMR, which denotes the difference between the hygroscopicity at 30° C. and 90% RH, which represent a typical temperature and humidity conditions in clothing resulting from a light to medium degree of work or a light to medium degree of exercise and that at 20° C. and 65% RH, which represent a typical outdoor air temperature and humidity conditions. A larger ΔMR value ensures a higher hygroscopic performance and higher comfortability when the clothes are worn.

It is preferable for the core-sheath composite yarn to have a ΔMR value of 5.0% or more. It is more preferably 7.0% or more and still more preferably 10.0% or more. If it is in this range, it will be possible to produce clothing that have reduced stuffiness and stickiness when worn and have high comfortability.

It is preferable for the core-sheath composite yarn to have a ΔMR retention rate of 70% or more and 100% or less after undergoing dry heat treatment at 150° C. for 1 hour. If it is in this range, it will be possible to produce clothing that can maintain moisture absorbing and releasing performance as well as high comfortability after undergoing repeated tumble drying.

A polyether ester amide copolymer to be used in the core contains both a hindered phenolic stabilizer, which is an antioxidant to capture radicals, and a hindered amine based stabilizer (hereinafter referred to as HALS type stabilizer) to make it possible to provide a core-sheath composite yarn characterized by depressed thermal degradation of the polyether ester amide copolymer even after undergoing repeated tumble drying to ensure a high durability and moisture absorbing and releasing performance as well as a soft texture.

The polyether ester amide copolymer used in the core contains poly(alkylene oxide) glycol, and when the poly(alkylene oxide) glycol is heated, radicals will be generated from the molecule and attack adjacent atoms to further generate radicals to cause chain reaction, and the reaction heat will work to increase the temperature up to as high as 200° C. As the molecular weight of the poly(alkylene oxide) glycol decreases, the molecular chain will be heated more easily to generate more radicals and generate more reaction heat.

The polyether ester amide copolymer contains a poly(alkylene oxide) glycol having a relatively low number average molecular weight of 300 to 3,000 and, accordingly, the polyether ester amide copolymer tends to undergo thermal degradation easily through the above mechanism, thus leading very easily to raw threads that are hard and brittle and have an inferior hygroscopic performance.

To avoid this, a hindered phenolic stabilizer, which is an antioxidant to capture radicals, is added to the polyether ester amide copolymer contained in the core. However, the addition of a hindered phenolic stabilizer alone will lead to progress of thermal degradation of the polyether ester amide copolymer due to the heat history in the spinning step (high temperature heating for melting the polymer and thermal setting after stretching) and the heat history in high-order processing steps (dyeing, thermal setting or the like of fabric), resulting in a large decrease in the effective component quantity of the antioxidant working to capture radicals remaining at the stages of fabrics and clothing. As they subsequently undergo repeated tumble drying, the polyether ester amide copolymer will suffer from further thermal degradation and the raw threads will become harder and more brittle and deteriorate in hygroscopic performance. Thus, the texture will become harder due to repeated washing and drying, leading to deterioration in durability and moisture absorbing and releasing performance.

Therefore, if a HALS (hindered amine light stabilizer) type stabilizer is used in combination to prevent a decrease in the effective component quantity of the antioxidant that works to capture radicals remaining in fabrics or clothing products, thermal degradation of the hindered phenolic stabilizer will be depressed to allow a soft texture, high durability, and moisture absorbing and releasing performance to be maintained after repeated tumble drying.

Regarding the quantity of the hindered phenolic stabilizer to be added when producing the core-sheath composite yarn, it preferably accounts for 1.0 wt % or more and 5.0 wt % or less relative to the weight of the polyether ester amide copolymer in the core. It more preferably accounts for 2 wt % or more and 4 wt % or less. If it is 1.0 wt % or more, it will be possible to produce raw threads that will not become hard or brittle or deteriorate in hygroscopic performance after undergoing repeated tumble drying. If it is 5.0 wt % or less, the yarn-making performance will be high and yellowing of the raw threads will be reduced.

The quantity of the residual hindered phenolic stabilizer in the core-sheath composite yarn is preferably 70% or more of the quantity of the hindered phenolic stabilizer (relative to the core-sheath composite yarn) added in the production process. It is more preferably 80% or more. If it is in this range, it will be possible to produce raw threads that will not become hard or brittle or deteriorate in hygroscopic performance after undergoing repeated tumble drying.

Regarding the quantity of the HALS type stabilizer to be added when producing the core-sheath composite yarn, it preferably accounts for 1.0 wt % or more and 5.0 wt % or less relative to the weight of the polyether ester amide copolymer in the core. It more preferably accounts for 1.5 wt % or more and 4.0 wt % or less. If it is 1.0 wt % or more, it will be possible to depress the thermal degradation of the hindered phenolic stabilizer used in combination. If it is 5.0 wt % or less, the yarn-making performance will be high and yellowing of raw threads will be reduced.

For the hindered phenolic stabilizer and HALS type stabilizer, the 5% weight loss temperature during thermogravimetric analysis is preferably 300° C. or more. If it is 300° C. or more, the stabilizer itself will suffer little degradation that may be caused by the heat history in the spinning step or the heat history in high-order processing steps to allow a significant effective component quantity of the antioxidant to be left to capture radicals remaining in fabric and clothing products so that the polyether ester amide copolymer will suffer little thermal degradation after undergoing repeated tumble drying and serve to maintain a soft texture and high durability and moisture absorbing and releasing performance, and therefore it is preferable.

Examples of such a hindered phenolic stabilizer include, for example, pentaery-thritoltetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (IR1010), (1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxyphenyl) benzene (AO-330), 1,3,5-tris-[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl] methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (IR3114), and N,N′-hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propane amide] (IR1098).

Examples of such a HALS type stabilizer include, for example, a polycondensate of dibutylamine-1,3,5-triazine, N,N-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylene diamine, and N-(2,2,6,6-tetramethyl-4-piperidyl)butyl amine (CHIMASSORB2020FDL), 4,7,N,N′-tetrakis [4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]-4,7-diaza-decane-1,10-diamine (CHIMASSORB119), poly[{6-(1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl) ((2,2,6,6-tetramethyl-4-piperidyl)imino) hexamethylene ((2,2,6,6-tetramethyl-4-piperidyl) imino (CHIMASSORB944).

The polyamide sheath component may contain, in the form of a copolymer or a mixture, various additives such as, for example, delustering agent, flame retardant, ultraviolet absorber, infrared ray absorbent, crystal nucleating agent, fluorescent whitening agent, antistatic agent, hygroscopic polymer, and carbon, as required such that the total additive content is 0.001% to 10 wt % of the total fiber quantity.

It is preferable for the core-sheath composite yarn to have an elongation percentage of 35% or more. It is more preferably 40% to 80%. If it is in this range, a high process passability will be ensured for high-order steps such as weaving, knitting, and false-twisting.

There are no specific limitations on the total fineness and number of filaments in the core-sheath composite yarn, and the resulting fabrics may have any desired cross-sectional shape to meet their purposes. In view of its use as long fiber material for clothing, multifilaments produced therefrom preferably have a total fineness of 5 decitex or more and 235 decitex or less and contain 1 or more and 144 or less filaments. The cross section may preferably be circular, triangle, flattened, Y-shaped, start-like, eccentric, or pasted type.

The core-sheath composite yarn can be produced by a generally known method such as melt-spinning and composite spinning, and typical methods are described below.

For example, polyamide (the sheath component) and a polyether ester amide copolymer (the core) are melted, weighed, and transported by a gear pump separately, and then they are combined by a common method into a composite flow having a core-sheath structure and discharged from a spinneret to produce threads, which are then cooled to room temperature by applying cooling air from a cooling apparatus such as chimney, bundled while supplying oil from an oil feeding apparatus, interlaced by a first fluid interlacing nozzle apparatus, and transported on a take-up roller and a stretching roller where the yarn is stretched according to the ratio of circumferential speeds of the take-up roller and the stretching roller. Subsequently, the yarn is heat-set by the heat of the stretching roller and wound up by a winder (winding-up apparatus).

In the spinning step, it is preferable for the spinning temperature to be 240° C. or more and 270° C. or less. A spinning temperature of 240° C. or more is preferable because the polyamide and polyether ester amide copolymer will have a melt viscosity suitable for melt-spinning. A temperature of 270° C. or less is preferable because the hindered phenolic stabilizer and the HALS type stabilizer can be performed effectively without undergoing thermal decomposition, thus serving to depress the thermal decomposition of the polyether ester amide copolymer.

For the core-sheath composite yarn, it is necessary for the core to account for 20 wt % to 80 wt % of the entire composite yarn. It is more preferably 30 wt % to 70 wt %. If it is in this range, it will be possible to stretch the polyamide in the sheath to an appropriate degree. It will be also possible to achieve a desired dyed color fastness and hygroscopic performance. If it is less than 20 wt %, a sufficient hygroscopic performance may not be achieved. If it is more than 80 wt %, on the other hand, cracking of the fiber surface may occur easily due to swelling in a hydrothermal atmosphere such as in the dyeing step, and in addition the polyamide in the sheath may be stretched excessively to cause thread breakage and fuzzing. For stable production of intended fibers, spinning and stretching that can cause excessive tension are not desirable because thread breakage and fuzzing may be caused.

The sheath is preferably formed of polyamide chips having a sulfuric acid relative viscosity of 2.3 or more and 3.3 or less. If it is in this range, it will be possible to stretch the polyamide in the sheath to an appropriate degree.

The polymer chips of the polyether ester amide copolymer used in the core preferably has an orthochlorophenol relative viscosity of 1.2 or more and 2.0 or less. An orthochlorophenol relative viscosity of 1.2 or more is preferable because an optimum stress will be applied to the sheath during spinning and accordingly, the crystallization of the polyamide in the sheath will be accelerated to ensure high strength.

Good methods for blending a hindered phenolic stabilizer or a HALS type stabilizer with a polyether ester amide copolymer include the dry blending method in which a hindered phenolic stabilizer or a HALS type stabilizer is attached to chips of a polyether ester amide copolymer and the master chip method in which master chips of a polyether ester amide copolymer mixed with a high concentration of a hindered phenolic stabilizer or HALS type stabilizer are prepared first in a twin screw extruder or a single screw extruder, followed by blending the master chips and polyether ester amide copolymer chips in the spinning step. Use of the master chips is preferable because a high concentration of a hindered phenolic stabilizer or HALS type stabilizer can be dispersed uniformly in the polymer.

The spinning conditions are preferably set up so that the speed of the threads taken up on the take-up roller (spinning speed) multiplied by the draw ratio, which is the ratio in circumferential speed between the take-up roller and the stretching roller, is 3,300 or more and 4,500 or less in the stretching step. It is more preferably 3,300 or more and 4,000 or less. This value represents the total quantity of stretching that the polymer undergoes as it is discharged from the spinneret, accelerated from the spinneret discharging linear speed to the circumferential speed of the take-up roller, and pulled further from the circumferential speed of the take-up roller to the circumferential speed of the stretching roller. If it is in this range, it will be possible to stretch the polyamide in the sheath to an appropriate degree. A value of 3,300 or more is preferable because it ensures accelerated crystallization of the polyamide in the sheath, leading to an improved raw thread strength and heat resistance. A value of 4,500 or less is preferable because it ensures moderate crystallization of the polyamide in the sheath, leading to a lower degree of thread breakage and fuzzing in the yarn-making step.

The thermal setting temperature on the stretching roller is preferably 110° C. or more and 160° C. or less. A temperature of 110° C. or more is preferable because it ensures accelerated crystallization of the nylon in the sheath, leading to improvement in strength and depression of tight winding by the drum. A temperature of 160° C. or less is preferable because it ensures depression of the thermal decomposition of the hindered phenolic stabilizer.

For the oil feeding step, the spinning oil solution fed by the oil feeding apparatus is preferably a non-aqueous oil solution. The polyether ester amide copolymer in the core is a highly hygroscopic polymer with a ΔMR value of 10% or more and, accordingly, the use of a non-aqueous oil solution is preferable because it allows gradual absorption of moisture from air, thus preventing significant swelling to ensure stable winding-up.

The core-sheath composite yarn has high hygroscopic performance and, accordingly, it is preferred for production of clothing. The intended fabric may be in the form of woven fabric, knitted fabric, nonwoven fabric and the like, as required to meet particular purposes. As described above, a larger ΔMR value ensures a higher hygroscopic performance and higher comfortability when the fabric is worn. In a fabric at least partly containing the core-sheath composite yarn, therefore, clothing with high comfortability can be produced by controlling the mixing rate of the core-sheath composite yarn to adjust the ΔMR value to 5.0% or more. Examples of such clothing include innerwear, sportswear, and other various clothing products.

EXAMPLES

Our yarns and fabrics are now described in more detail with reference to examples. The methods used for the measurement of characteristic values are as described below.

(1) Sulfuric Acid Relative Viscosity

First, 0.25 g of a specimen was dissolved in sulfuric acid with a concentration of 98 wt % such that it would account for 1 g in 100 ml, and the efflux time (T1) through an Ostwald type viscometer was measured at 25° C. Subsequently, the efflux time (T2) of the sulfuric acid with a concentration of 98 wt % alone was measured. The ratio of T1 to T2, i.e., T1/T2, was adopted as sulfuric acid relative viscosity.

(2) Orthochlorophenol Relative Viscosity

First, 0.5 g of a specimen was dissolved in orthochlorophenol such that it accounts for 1 g in 100 ml, and the efflux time (T1) through an Ostwald type viscometer was measured at 25° C. Subsequently, the efflux time (T2) of the orthochlorophenol alone was measured. The ratio of T1 to T2, i.e., T1/T2, was adopted as sulfuric acid relative viscosity.

(3) Fineness

A fiber specimen was set on a sizing reel with a circumference of 1.125 m and rotated 200 times to prepare a loop like hank, and then the hank was dried in a hot air drier (105±2° C. for 60 minutes) and weighed in a balance, followed by multiplying the weight by an official moisture regain to calculate the fineness. The official moisture regain of the core-sheath composite yarn was assumed to be 4.5%.

(4) Strength and Elongation Percentage

A fiber specimen was subjected to measurement using TENSILON (registered trademark) UCT-100 manufactured by Orientec Co., Ltd. under the constant stretching rate conditions specified in JIS L1013 (Chemical fiber filament test method, 2010). The elongation percentage was determined from the elongation at the maximum strength point on the tensile strength vs. elongation curve. The strength is calculated by dividing the maximum strength by the fineness. For strength and elongation percentage, ten measurements were taken and their average was adopted.

(5) Strength After Dry Heat Treatment

A fiber specimen was set on a sizing reel with a circumference of 1.125 m and rotated 200 times to prepare a loop like hank, and then the hank was heat-treated in a hot air drier (150±2° C. for 60 minutes), followed by calculating the strength of the dry-heat-treated specimen as described in paragraph (4).

(6) Strength Retention Rate After Dry Heat Treatment

To represent the difference in strength between before and after the dry heat treatment, the strength retention rate of a heat-treated specimen was calculated by the equation blow:

(strength after dry heat treatment/strength before dry heat treatment)×100.

(7) 5% Weight Loss Temperature

A thermogravimetric analyzer (TGA7, manufactured by Perkin Elmer) was used for the measurement. In a nitrogen atmosphere, a 10 mg specimen was heated from 30° C. to 400° C. at a heating rate of 10° C./min, followed by calculating the temperature at the point of 5% weight reduction.

(8) Quantity of Residual Hindered Phenolic Stabilizer (Relative to Core-Sheath Composite Yarn) A. Preparation of Standard Solution

In a 20 mL measuring flask, 0.02 g of a hindered phenolic stabilizer was weighed out and 2 mL of chloroform was added to dissolve it, followed by adding tetrahydrofuran (THF) to volume (undiluted standard solution: about 1,000 μg/mL). The original standard solution was diluted appropriately with acetonitrile to prepare a standard solution.

B. Preparation of Additive Standard Solution

In a 10 mL measuring flask, 0.01 g of a hindered phenolic stabilizer was weighed out and 2 mL of chloroform was added to dissolve it, followed by adding tetrahydrofuran (THF) to volume (standard solution for adding hindered phenolic stabilizer: about 1,000 μg/mL).

C. Preparation of Specimen Solution (n=2)

-   a. A 0.1 g portion of a fiber specimen was dissolved in 1 mL of     hexafluoroisopropanol (HFIP) and 2 mL of chloroform was added and     dissolved. -   b. A 40 mL volume of tetrahydrofuran (THF) was added gradually (the     polymer was insolubilized). -   c. Filtration was performed through a paper filter and the solution     obtained was condensed and exsiccated. -   d. A 1 mL volume of HFIP was added to the residue to dissolve it and     the resulting solution was transferred to a 10 mL measuring flask. -   e. The container used above was washed with THF and the washings     were added to 10 mL. -   f. Filtration was performed through a PTFE membrane filter with a     pore size of 0.45 μm and the resulting solution was adopted as     specimen solution.     Pre-treatment was performed without using a specimen to provide a     blank test solution.

D. LC/UV and LC/ELSD Analysis Conditions

-   LC system: LC10A (manufactured by Shimadzu Corporation) -   Column: Asahipak ODP-40 4D 4.6×150 mm, 4 μm (manufactured by Showa     Denko K.K.) -   Mobile phase: A—[28% aqueous ammonia/methanol=9/1,000]/water=1/1     -   B—0.1% triethyl amine THF solution -   Time program

0 to 3 min B: 50% 3 to 10 min B: 50% --> 70% 10 to 15 min B: 70% --> 90% 15 to 20 min B: 90% --> 100%

-   Flow rate: 1.0 mL/min -   Injection rate: 20 μL -   Column temperature: 45° C. -   Detection: hindered phenolic stabilizer UV 280 nm

(9) Preparation of Cylindrical Knitted Fabric

A cylindrical knitted fabric sample was produced using a cylindrical knitting machine while adjusting the density to 50. If the fiber is low in the corrected weight based fineness, yarn doubling is performed appropriately so that the fiber fed to the cylindrical knitting machine would have a total fineness of 50 to 100 decitex. If the total fineness is more than 100 decitex, a single yarn was fed to the cylindrical knitting machine and the density was adjusted to 50 as above.

(10) ΔMR

About 1 to 2 g of the cylindrical knitted fabric was weighed out in a weighing bottle, dried by storage at 110° C. for 2 hours, and weighed (W0). Subsequently, the target substance was maintained at 20° C. and a relative humidity of 65% for 24 hours and then weighed (W65). This was maintained at 30° C. and a relative humidity of 90% for 24 hours and then weighed (W90). Calculations were made by the equations below:

MR65=[(W65−W0)/W0]×100%   (1)

MR90=[(W90−W0)/W0]×100%   (2)

ΔMR=MR90−MR65   (3).

(11) ΔMR After Dry Heat Treatment

The cylindrical knitted fabric sample was heat-treated (150±2° C. for 60 minutes) in a hot air drier and then its moisture absorbing and releasing properties were measured, followed by making calculations.

(12) ΔMR Retention Rate After Dry Heat Treatment

To represent the difference in ΔMR between before and after the dry heat treatment, the ΔMR retention rate of a dry-heat-treated specimen was calculated by the equation below:

(ΔMR after dry heat treatment/ΔMR before dry heat treatment)×100.

(13) Tumble Drying

The cylindrical knitted fabric sample was dried at a temperature of 80° C. for 1 hour in a type-A1 tumble drying machine as specified in JIS L1930 (2014, household washing test method) Appendix G. This procedure was repeated 10 times.

(14) Texture Evaluation

The texture of the tumble-dried cylindrical knitted fabric sample was evaluated according to the four stage criterion given below. A specimen rated as A or higher was assumed to be acceptable.

-   S: The texture is just as soft as before tumble drying. -   A: The texture is nearly as soft as before tumble drying. -   B: The texture is a little harder than before tumble drying. -   C: The texture is significantly harder and stiffer than before     tumble drying.

(15) Durability Evaluation

The durability of a tumble-dried cylindrical knitted fabric sample was evaluated according to Method A (Muhlen type method) specified in “8.18 Bursting strength” of JIS L1096 (2010, Fabric test method for woven fabrics and knitted fabrics). A specimen rated as A or higher was assumed to be acceptable.

-   S: 200 kPa or more -   A: 150 kPa or more and less than 200 kPa -   C: less than 150 kPa

(16) Hygroscopicity Retention Property

The value of ΔMR, which is defined in paragraph (10), of a cylindrical knitted fabric sample was measured before and after tumble drying, followed by calculating the retention rate. A sample rated as A or higher was assumed to be acceptable.

-   S: 80% or more -   A: 70% or more and less than 80% -   C: less than 70%

Example 1

A polyether ester amide copolymer containing nylon 6 as polyamide component and polyethylene glycol with a molecular weight of 1,500 as polyether component with a molar ratio of 24% to 76% between nylon 6 and polyethylene glycol (MH1657, manufactured by Arkema K.K., orthochlorophenol relative viscosity 1.69) was adopted, and chips of the polyether ester amide copolymer used as core material. First, master chips prepared by adding a hindered phenolic stabilizer (IR1010, manufactured by BASF, 5% weight loss temperature 351° C.) and a HALS type stabilizer (CHIMASSORB2020FDL, manufactured by BASF, 5% weight loss temperature 404° C.) to high concentrations to the polyether ester amide copolymer and chips of the polyether ester amide copolymer were blended in a twin screw extruder so that the hindered phenolic stabilizer (IR1010) and HALS type stabilizer (CHIMASSORB2020FDL) would account for 2.0 wt %/2.0 wt %, respectively, of the core.

As the polyamide component, chips of nylon 6 with a sulfuric acid relative viscosity of 2.71 were used in the sheath.

The polyether ester amide copolymer adopted as core component and the nylon 6 adopted as sheath component were melted at a spinning temperature of 260° C. and spun through a spinneret designed for concentric circular core-sheath composite yarn at a core/sheath ratio (wt %) of 30/70. The rotating speed of the gear pump was controlled to produce a core-sheath composite yarn having a total fineness of 56 dtex and the threads were cooled and solidified in a thread cooling apparatus, fed with oil from a non-aqueous oil solution feeding apparatus, interlaced in a first fluid interlacing nozzle apparatus, stretched by a take-up roller (first roller) having a circumferential speed of 2,405 m/min and a stretching roller (second roller) having a circumferential speed of 3,608 m/min, thermally set by the stretching roller at 150° C., and wound up at a speed of 3,500 m/min to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 1.

For the resulting core-sheath composite yarn, the proportion of the residual hindered phenolic stabilizer was 88%, and the strength retention rate after dry heat treatment and the ΔMR retention rate after dry heat treatment were 65% and 75%, respectively. After undergoing repeated tumble drying, the raw threads in the resulting core-sheath composite yarn hardly became hard or brittle and maintained a soft texture and a high durability and moisture absorbing and releasing performance.

Example 2

Except for adjusting the spinning temperature to 270° C., the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 1.

For the resulting core-sheath composite yarn, the proportion of the residual hindered phenolic stabilizer was 75%, and the strength retention rate after dry heat treatment and the ΔMR retention rate after dry heat treatment were 60% and 72%, respectively.

Example 3

Except for adjusting the spinning temperature to 240° C., the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 1.

The proportion of the residual hindered phenolic stabilizer in the resulting core-sheath composite yarn was a high 93%, and the strength retention rate after heat treatment and the ΔMR retention rate after heat treatment were high 70% and 77%, respectively.

Example 4

Except for adjusting the stretching roller temperature to 120° C., the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 1.

The proportion of the residual hindered phenolic stabilizer in the resulting core-sheath composite yarn was a high 90%, and the strength retention rate after heat treatment and the ΔMR retention rate after heat treatment were high 67% and 77%, respectively.

Example 5

Except for performing the spinning at a core/sheath ratio of 50/50 (parts by weight), the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 1.

The proportion of the residual hindered phenolic stabilizer in the resulting core-sheath composite yarn was a high 85%, and the strength retention rate after heat treatment and the ΔMR retention rate after heat treatment were high 63% and 72%, respectively.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Core component polymer polyether ester polyether ester polyether ester polyether ester polyether ester amide copolymer amide copolymer amide copolymer amide copolymer amide copolymer relative viscosity 1.69 1.69 1.69 1.69 1.69 Sheath component polymer nylon 6 nylon 6 nylon 6 nylon 6 nylon 6 relative viscosity 2.71 2.71 2.71 2.71 2.71 Core-sheath ratio core/sheath 30/70 30/70 30/70 30/70 50/50 Hindered phenolic type IR1010 IR1010 IR1010 IR1010 IR1010 stabilizer content (wt %) 2.00 2.00 2.00 2.00 2.00 5% weight loss 351 351 351 351 351 temperature (° C.) HALS type stabilizer type CHIMASSROB CHIMASSROB CHIMASSROB CHIMASSROB CHIMASSROB 2020FDL 2020FDL 2020FDL 2020FDL 2020FDL content (wt %) 2.00 2.00 2.00 2.00 2.00 5% weight loss 404 404 404 404 404 temperature (° C.) Yarn-making conditions spinning temperature (° C.) 260 270 240 260 260 take-up speed (m/min) 2405 2405 2405 2405 2405 draw ratio 1.5 1.5 1.5 1.5 1.5 product 3608 3608 3608 3608 3608 thermal setting 150 150 150 120 150 temperature (° C.) Physical properties of fineness (dtex) 56 56 56 56 56 raw thread elongation percentage (%) 50 50 50 50 48 proportion of 88 75 93 90 85 residual hindered phenolic stabilizer (%) Strength retention strength (cN/dtex) 3.5 3.6 3.3 3.3 3.2 strength after 2.3 2.2 2.3 2.2 2.0 heat treatment (cN/dtex) retention rate (%) 65 60 70 67 63 Hygroscopic ΔMR(%) 7.5 7.2 7.7 7.5 11.7 performance retention ΔMR after 5.6 5.2 5.9 5.8 8.4 heat treatment (%) retention rate (%) 75 72 77 77 72 Evaluation of cylindrical texture A A S A A knitted fabric after durability S S S S S tumble drying hygroscopicity retention A A A A A

Example 6

Except for performing the spinning step at a core/sheath ratio of 70/30 (parts by weight), the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 2.

The proportion of the residual hindered phenolic stabilizer in the resulting core-sheath composite yarn was a high 83%, and the strength retention rate after heat treatment and the ΔMR retention rate after heat treatment were high 60% and 70%, respectively.

Example 7

Except for adjusting the hindered phenolic stabilizer (IR1010) and HALS type stabilizer (CHIMASSORB2020FDL) to 3.0 wt % and 2.0 wt %, respectively, relative to the weight of the core, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 2.

The proportion of the residual hindered phenolic stabilizer in the resulting core-sheath composite yarn was a high 86%, and the strength retention rate after heat treatment and the ΔMR retention rate after heat treatment were high 70% and 78%, respectively.

Example 8

Except for adjusting the hindered phenolic stabilizer (IR1010) and HALS type stabilizer (CHIMASSORB2020FDL) to 3.0 wt % and 3 wt %, respectively, relative to the weight of the core, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 2.

The proportion of the residual hindered phenolic stabilizer in the resulting core-sheath composite yarn was a high 90%, and the strength retention rate after heat treatment and the ΔMR retention rate after heat treatment were high 75% and 80%, respectively.

Example 9

Except for adjusting the hindered phenolic stabilizer (IR1010) and HALS type stabilizer (CHIMASSORB2020FDL) to 4 wt % and 4 wt %, respectively, relative to the weight of the core, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 2.

The proportion of the residual hindered phenolic stabilizer in the resulting core-sheath composite yarn was a high 93%, and the strength retention rate after heat treatment and the ΔMR retention rate after heat treatment were high 80% and 85%, respectively.

Example 10

Except for adjusting the hindered phenolic stabilizer (IR1010) and HALS type stabilizer (CHIMASSORB2020FDL) to 1 wt % and 1 wt %, respectively, relative to the weight of the core, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 2.

The proportion of the residual hindered phenolic stabilizer in the resulting core-sheath composite yarn was a high 75%, and the strength retention rate after heat treatment and the ΔMR retention rate after heat treatment were high 55% and 70%, respectively.

TABLE 2 Example 6 Example 7 Example 8 Example 9 Example 10 Core component polymer polyether ester polyether ester polyether ester polyether ester polyether ester amide copolymer amide copolymer amide copolymer amide copolymer amide copolymer relative viscosity 1.69 1.69 1.69 1.69 1.69 Sheath component polymer nylon 6 nylon 6 nylon 6 nylon 6 nylon 6 relative viscosity 2.71 2.71 2.71 2.71 2.71 Core-sheath ratio core/sheath 70/30 30/70 30/70 30/70 30/70 Hindered phenolic type IR1010 IR1010 IR1010 IR1010 IR1010 stabilizer content (wt %) 2.00 3.00 3.00 4.00 1.00 5% weight loss 351 351 351 351 351 temperature (° C.) HALS type stabilizer type CHIMASSROB CHIMASSROB CHIMASSROB CHIMASSROB CHIMASSROB 2020FDL 2020FDL 2020FDL 2020FDL 2020FDL content (wt %) 2.00 2.00 3.00 4.00 1.00 5% weight loss 404 404 404 404 404 temperature (° C.) Yarn-making conditions spinning temperature (° C.) 260 260 260 260 260 take-up speed (m/min) 2405 2405 2405 2405 2405 draw ratio 1.5 1.5 1.5 1.5 1.5 product 3608 3608 3608 3608 3608 thermal setting 150 150 150 150 150 temperature (° C.) Physical properties of fineness (dtex) 56 56 56 56 56 raw thread elongation percentage (%) 48 52 47 47 48 proportion of 83 86 90 93 75 residual hindered phenolic stabilizer (%) Strength retention strength (cN/dtex) 3.6 3.6 3.5 3.2 3.4 strength after 2.2 2.5 2.8 2.6 1.9 heat treatment (cN/dtex) retention rate (%) 60 70 75 80 55 Hygroscopic ΔMR(%) 15.2 7.7 7.9 8.0 7.1 performance retention ΔMR after 10.6 6.0 6.3 6.8 5.0 heat treatment (%) retention rate (%) 70 78 80 85 70 Evaluation of cylindrical texture A S S S A knitted fabric after durability S S S S A tumble drying hygroscopicity retention A A S S A

Comparative Example 1

Except for omitting the addition of a hindered phenolic stabilizer and a HALS type stabilizer and adjusting the strength retention rate after dry heat treatment to 30%, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 3.

The resulting core-sheath composite yarn had a ΔMR retention rate after dry heat treatment of 50%. After undergoing repeated tumble drying, the raw threads in the resulting core-sheath composite yarn were found to be hard or brittle and have a stiff texture and an inferior durability.

Comparative Example 2

Except for omitting the addition of a HALS type stabilizer (CHIMASSORB2020FDL) and adjusting the strength retention rate after dry heat treatment to 40%, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 3.

The proportion of the residual hindered phenolic stabilizer in the resulting core-sheath composite yarn was a low 40%, and the ΔMR retention rate after heat treatment was 55%. After undergoing repeated tumble drying, the raw threads in the resulting core-sheath composite yarn were found to be hard or brittle and have a stiff texture and an inferior durability. In addition, the hygroscopic performance deteriorated as a result of thermal degradation of the polyethylene glycol component contained in the polyether ester amide copolymer.

Comparative Example 3

Except for omitting the addition of a hindered phenolic stabilizer (IR1010) and adjusting the strength retention rate after dry heat treatment to 33%, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 3.

The resulting core-sheath composite yarn had a ΔMR retention rate after heat treatment of 52%. After undergoing repeated tumble drying, the raw threads in the resulting core-sheath composite yarn were found to be hard or brittle and have a stiff texture and an inferior durability. In addition, the hygroscopic performance deteriorated as a result of thermal degradation of the polyethylene glycol component contained in the polyether ester amide copolymer.

Comparative Example 4

Except for adjusting the hindered phenolic stabilizer (IR1010) and HALS type stabilizer (CHIMASSORB2020FDL) to 0.5 wt % and 0.5 wt %, respectively, relative to the weight of the core and adjusting the strength retention rate after dry heat treatment to 45%, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 3.

The proportion of the residual hindered phenolic stabilizer in the resulting core-sheath composite yarn was a low 60%, and the ΔMR retention rate after heat treatment was 65%. After undergoing repeated tumble drying, the raw threads in the resulting core-sheath composite yarn were found to be hard or brittle and have a stiff texture and an inferior durability. In addition, the hygroscopic performance deteriorated as a result of thermal degradation of the polyethylene glycol component contained in the polyether ester amide copolymer.

Comparative Example 5

Except for using a hindered phenolic stabilizer with a 5% weight loss temperature of 223° C. (IR1135, manufactured by BASF) and adjusting the strength retention rate after dry heat treatment to 40%, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 3.

For the resulting core-sheath composite yarn, the proportion of the residual hindered phenolic stabilizer was 50% and the ΔMR retention rate after dry heat treatment was 60%. After undergoing repeated tumble drying, the raw threads in the resulting core-sheath composite yarn were found to be hard or brittle and have a stiff texture and an inferior durability. In addition, the hygroscopic performance deteriorated as a result of thermal degradation of the polyethylene glycol component contained in the polyether ester amide copolymer.

Comparative Example 6

Except for using a HALS type stabilizer with a 5% weight loss temperature of 275° C. (Adeka Stab LA-81, manufactured by Adeka Corporation) and adjusting the strength retention rate after dry heat treatment to 45%, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn. Physical properties of the resulting fiber are shown in Table 3.

For the resulting core-sheath composite yarn, the proportion of the residual hindered phenolic stabilizer was 63% and the ΔMR retention rate after dry heat treatment was 65%. After undergoing repeated tumble drying, the raw threads in the resulting core-sheath composite yarn were found to be hard or brittle and have a stiff texture and an inferior durability. In addition, the hygroscopic performance deteriorated as a result of thermal degradation of the polyethylene glycol component contained in the polyether ester amide copolymer.

Comparative Example 7

Except for replacing the hindered phenolic stabilizer with a phosphorus-based antioxidant (Adeka Stab PEP-36, manufactured by Adeka Corporation, 5% weight loss temperature 316° C.) and adjusting the strength retention rate after dry heat treatment to 45%, the same procedure as in Example 1 was carried out to provide a 56-decitex, 24-filament core-sheath composite yarn.

The resulting fiber had a fineness of 56 decitex, an elongation percentage of 50%, a strength of 3.0 cN/dtex, a ΔMR value of 6.7%, and a ΔMR retention rate after dry heat treatment of 60%.

After undergoing repeated tumble drying, the raw threads in the resulting core-sheath composite yarn were found to be hard or brittle and have a stiff texture and an inferior durability and hygroscopicity retention property. Thus, the phosphorus-based antioxidant did not work effectively.

TABLE 3 Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Core component polymer polyether ester polyether ester polyether ester polyether ester amide amide amide amide copolymer copolymer copolymer copolymer relative viscosity 1.69 1.69 1.69 1.69 Sheath polymer nylon 6 nylon 6 nylon 6 nylon 6 component relative viscosity 2.71 2.71 2.71 2.71 Core-sheath ratio core/sheath 30/70 30/70 30/70 30/70 Hindered phenolic type IR1010 IR1010 IR1010 IR1010 stabilizer content (wt %) 0 2.00 0 0.50 5% weight loss temperature (° C.) 351 351 351 351 HALS type type CHIMASSROB CHIMASSROB CHIMASSROB CHIMASSROB stabilizer 2020FDL 2020FDL 2020FDL 2020FDL content (wt %) 0 0 2.00 0.50 5% weight loss temperature (° C.) 404 404 404 404 Yarn-making spinning temperature (° C.) 260 260 260 260 conditions take-up speed (m/min) 2405 2405 2405 2405 draw ratio 1.5 1.5 1.5 1.5 product 3608 3608 3608 3608 thermal setting temperature (° C.) 150 150 150 150 Physical fineness (dtex) 56 56 56 56 properties of raw elongation percentage (%) 43 45 44 48 thread proportion of residual hindered 0 40 0 60 phenolic stabilizer (%) Strength retention strength (cN/dtex) 3.0 3.2 3.2 3.4 strength after 0.9 1.3 1.1 1.5 heat treatment (cN/dtex) retention rate (%) 30 40 33 45 Hygroscopic ΔMR (%) 6.7 7.0 6.9 7.2 performance ΔMR after 3.4 3.9 3.6 4.7 retention heat treatment (%) retention rate (%) 50 55 52 65 Evaluation of texture C C C B cylindrical knitted durability C C C C fabric after tumble hygroscopicity retention C C C C drying Comparative Comparative Comparative Example 5 Example 6 Example 7 Core component polymer polyether ester polyether ester polyether ester amide amide amide copolymer copolymer copolymer relative viscosity 1.69 1.69 1.69 Sheath polymer nylon 6 nylon 6 nylon 6 component relative viscosity 2.71 2.71 2.71 Core-sheath ratio core/sheath 30/70 30/70 30/70 Hindered phenolic type IR1135 IR1010 Adeka Stab stabilizer PEP-36 content (wt %) 2.00 2.00 2.00 5% weight loss temperature (° C.) 223 351 316 HALS type type CHIMASSROB Adeka Stab CHIMASSROB stabilizer 2020FDL LA-81 2020FDL content (wt %) 2.00 2.00 2.00 5% weight loss temperature (° C.) 404 275 404 Yarn-making spinning temperature (° C.) 260 260 260 conditions take-up speed (m/min) 2405 2405 2405 draw ratio 1.5 1.5 1.5 product 3608 3608 3608 thermal setting temperature (° C.) 150 150 150 Physical fineness (dtex) 56 56 56 properties of raw elongation percentage (%) 50 50 50 thread proportion of residual hindered 50 63 — phenolic stabilizer (%) Strength retention strength (cN/dtex) 3.2 3.1 3.0 strength after 1.3 1.4 1.4 heat treatment (cN/dtex) retention rate (%) 40 45 45 Hygroscopic ΔMR (%) 6.8 6.6 6.7 performance ΔMR after 4.1 4.3 4.0 retention heat treatment (%) retention rate (%) 60 65 60 Evaluation of texture C B B cylindrical knitted durability C C C fabric after tumble hygroscopicity retention C C C drying

INDUSTRIAL APPLICABILITY

We provide a core-sheath composite yarn high in hygroscopic performance, higher in comfortability than natural fibers, and able to maintain a soft texture, high durability, and moisture absorbing and releasing performance after undergoing repeated washing and drying. 

1-3. (canceled)
 4. A hygroscopic core-sheath composite yarn comprising polyamide as a sheath polymer and a polyether ester amide copolymer as a core polymer, the yarn having a strength retention rate of 50% or more after undergoing dry heat treatment at 150° C. for 1 hour.
 5. The hygroscopic core-sheath composite yarn as set forth in claim 4, having a ΔMR value of 5.0% or more and a ΔMR retention rate of 70% or more after undergoing dry heat treatment at 150° C. for 1 hour.
 6. A fabric comprising, at least partly, a hygroscopic core-sheath composite yarn as set forth in claim
 4. 7. A fabric comprising, at least partly, a hygroscopic core-sheath composite yarn as set forth in claim
 5. 